The invention relates to a plug connector for mounting on a circuit board and having a carrier body in which at least one surface mounting contact member is disposed which comprises, at one end, a plug-in region for connection with a complementary plug connector and,-at the other end, a connecting region which may be connected with the conductor track of a circuit board.
The surface mounting technology offers some advantages over conventional plug connectors which are provided with pass-through mounting contact members, both during the mounting process and as regards the transmission speed for signals from the surface mounting contact member to the conductor track of the circuit board. In order to accomplish a reliably soldered connection, particular attention must be paid to the coplanarity of the terminal ends during the manufacturing process for the plug connectors. It has turned out that the height deviation of the connecting region must not exceed 0.1 mm if all connections shall be safely soldered. However, such slight tolerances may only be ensured either via a very expensive manufacturing process leading to a product which reliably keeps to the corresponding tolerances, or via a sorting process following the manufacturing process, in which all those plug connectors are sorted out which do not keep to the required tolerances. However, this leads to a high reject rate and, accordingly, to high overall production costs.
Another problem with regard to surface mounted contact members consists in that the soldered joint between the contact member and the circuit board is less rigid than a soldered joint with through-type contact members, more particularly under shear stress. On the one hand, this fact is critical in view of the forces acting on the plug connector during insertion into a complementary plug connector and, on the other hand, in view of mechanical stresses arising from differences in the thermal expansion of the circuit board and the plug connector or due to flexure of the circuit board.
Therefore it is the object underlying the invention to further develop a plug connector of the type initially mentioned to the effect that despite low manufacturing expenditure a reliable connection is guaranteed between the connecting region of the surface mounting contact member and the conductor track of the circuit board and that significant mechanical forces are prevented from acting on the soldered connection after soldering.
In order to meet this object, it is provided for in accordance with the invention that the contact member comprises a connecting member which is connected with the connecting region in a mechanically flexible and electrically conductive manner and may be soldered to the conductor track of the circuit board. The basic idea underlying the plug connector according to the invention resides in configuring the surface mounting contact member in multiple parts and in taking advantage of a predetermined slidability between the different parts, i.e. the actual contact member and the connecting member in particular, for tolerance compensation during assembly of the plug connector on the one hand and for permanent movability during operation of the plug connector on the other hand. The tolerance compensation, which is now realized automatically, reduces manufacturing process requirements so that there result lower costs. Mechanical decoupling between the circuit board and the surface mounting contact member increases the durability of the soldering points since there occurs a relative displacement between the connecting member and the contact member, but no mechanical strain on the soldering points when certain mechanical stresses between the circuit board and the contact member are exceeded.
Preferably, it is provided that the connecting member is slidably mounted on the connecting region. Thus, the connecting member may be attached to the surface mounting contact member before the plug connector is mounted on the circuit board already and need not be handled as a separate component during the assembly process.
According to the preferred embodiment, it is provided that, before the plug connector is mounted on the circuit board, the connecting member is in a mounting position in which it projects farther from the plug connector than after mounting. In this manner, the desired tolerance compensation results automatically when the plug connector is put onto the circuit board since the projecting connecting members are shifted into the correct position during putting-on.
According to the preferred embodiment, it is further provided that the connecting member is a resilient clamp engaging the connecting region. On the one hand, this spring effect may ensure that the desired contact force between the clamp and the connecting region of the surface mounting contact member exists even after a long operating time. On the other hand, one may adjust via the spring force amount which mechanical stress must act between the surface mounting contact member and the connecting member before there will occur a relative displacement.
According to a preferred variant, it is provided that the connecting member is formed to be spherical. This makes it possible to contact the connecting region from almost any direction since there always result two diametrically opposite contact points on the connecting region, irrespective of slight relative displacements.
The contact member is preferably provided with an insulating body which constitutes a guide for the clamp. The guide ensures that the clamp is in the desired position before assembly of the plug connector so that it is automatically shifted from the mounting position into the correct position for soldering. The guide is more particularly required in conjunction with the spherical connecting region since the latter cannot provide any guide for the clamp.
The insulating body is preferably provided with contact faces for the clamp, which are opposite each other at a spacing larger than the corresponding dimension of the clamp in this region. This dimensioning of the parts relative to each other not only enables a translatory shifting of the clamp on the guide, but also a pivot and tilt movement which may be necessary for the compensation of mechanical stresses which may result from bending of the circuit board or from differences in the thermal expansion between the plug connector and the circuit board.
According to an alternative variant, it is provided that the connecting region has a rectangular cross-section. In this case, a guide for the connecting member is realized due to the shape of the connecting region already. The alternative variant preferably provides that the clamp is provided with several guide surfaces which may engage opposite edges of the connecting regions. This makes sure that the clamp does not laterally slip off the connecting region. The guide surfaces may be formed on bent-off noses of the clamp.
According to the preferred embodiment, it is provided that the resilient clamp comprises two legs engaging the connecting region, and a bottom connecting the two legs with each other and facing towards the circuit board, and that the bottom is provided with a spacer which ensures a predetermined spacing between the bottom and the circuit board. The spacer prevents the bottom of the clamp from bearing against the circuit board during assembly of the plug connector and from fully forcing the solder paste, which had previously been applied to the circuit board, away in this region, which would result in an inadequate solder joint.
It is preferably provided that the spacer is formed as a raised portion which may bear with its apex against the circuit board. The apex of the raised portion forms a tip which reliably penetrates the solder paste. This makes sure that the spacer actually bears against the circuit board rather than against a solder paste pad so that the correct spacing between the bottom of the clamp and the circuit board is ensured.
According to an alternative embodiment, it may be provided that the connecting member is connected with the connecting region via a bond wire. Thus, a further additional component is used in this case in order to create the electrically conductive connection between the connecting member and the connecting region of the contact member. The bond wire enables relative movability of the parts.
According to the preferred embodiment of the invention, there is further provided at least one pass-through mounting contact member. In this manner, two advantages result therefrom: on the one hand, the pass-through mounting contact member enables a sort of preliminary fixing of the plug connector after it has been put onto the circuit board and before soldering. On the other hand, the pass-through mounting contact member ensures, due to its higher holding force in the circuit board, good mechanical fixing of the plug connector so that there is less strain on the soldered joints of the surface mounting contact members from forces acting on the plug connector.
Preferably, the pass-through mounting contact member is an earth contact and the surface mounting contact member is a signal contact. This configuration takes into account the advantages offered by a surface mounting contact member in view of signal velocity; maximum signal velocity is of secondary importance for an earth contact.
According to one embodiment of the invention, the plug connector is a card-edge plug connector. Plug connectors of that kind are used for a multipole and pluggable connection between a circuit board and a cable and, respectively, another circuit board for the transmission of electrical signals. The contact members are disposed in an insulating body in rows and columns. Via a suitable combination of surface mounting contact members and pass-through mounting contact members there may be obtained a card-edge plug connector which is both anchored on the circuit board with high mechanical strength, namely by means of the pass-through mounting contact members, and offers a high signal transmission velocity, namely due to the surface mounting contact members. No longer does the problem occur, which had hitherto arisen in the prior art, namely that the surface mounting contact members of a card-edge plug connector are shear-strained due to the location of the plug connector since, on the one hand, the pass-through mounting contact members introduce a large part of the occurring forces directly into the circuit board and, on the other hand, a possible relative displacement between the plug connector and the circuit board does not result in any stress on the soldered joints between the surface mounting contact members and the conductor tracks since the multi-part configuration of the contact member enables a relative displacement with the connecting member.
According to a further embodiment, it is provided that the plug connector is a coaxial-contact plug connector. This configuration also takes advantage of the combination of a surface mounting contact member and a pass-through mounting contact member, more particularly when the surface mounting contact member constitutes an inner conductor of a coaxial contact member and the pass-through mounting contact member is an earth sheet metal connected with an outer conductor of the coaxial contact. Reference is made to the above explanations in respect of the advantages of this combination of a signal contact and an earth contact.
Advantageous configurations of the invention may be taken from the sub-claims.